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only blows out floor vent

Sgyates27253

Sgyates27253

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1987 k5 air system only blows out floor vent..move lever to defrost still just blows out floor vent ..
 
Blend door adjusts between hot and cold (amount of air pulled through heater core vs. evap). There are a few vacuum motors that select the mode, based on the vacuum switch behind the mode switch in the dash. Of course, you have to have vacuum behind the dash for anything to work. Check these:

https://ck5.com/forums/threads/not-defrost.323543/#post-3586985
https://ck5.com/forums/threads/vacuum-line-routing-for-defrost-function.326525/
https://ck5.com/forums/threads/a-c-vent-controls.323319/#post-3580021
 
Thank.. .any one know of any good schematics of system..
 
Mine didn't work for the longest time, i finally got to lookin at it,,, didn't have the vacuum source under the hood hooked up for the blend door control. :-P
 
Yeah, start underhood and make sure vacuum is coming through the firewall before you start underhood. Could be a 1 minute fix.
 
On my '85 Burb with A/C I have to manually move the lever under the dash in the center heater duct to switch from defrost to heat,the vacuum can that operates the "door" in the heater box,must have a dead diaphram,everything is getting vacuum,and I hear it hissing from the "can"...I never bothered to try replacing it,truck hasn't left my driveway since I owned it ..
 
Fixed it..vaccum hose..doing whole dash replacement..all led new dash new speakers and sealed up all duct work..
 
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